LEDs characterized by high energy conversion efficient, small in size and long-life have widely been applied to various electronic products. Usually, LEDs are used for indictors or lighting, or are used in a display device for display images. In brief, a LED has an illumination layer and at least two types of semiconductor layers, so manufacturers can produce different color LEDs by adjusting the material of the illumination layer and the materials of the semiconductor layers.
However, the semiconductor layers in various regions of the same wafer may have different epitaxial qualities during an epitaxy process. The uneven quality of epitaxy may cause the occurrence of deviation to the peak wavelengths of light emitted by LEDs that are driven. That is, a certain batch of LEDs, initially expected to emit the same color light, have a difference in color of light therebetween due to their uneven epitaxial qualities; the difference in color of light is even sensible to human's eyes.
Moreover, the microminiaturization of LEDs is very expectative in the next generation of semiconductor technology. The existing technology has been able to shrink LEDs down to a micrometer scale. However, since the sizes of LEDs are getting smaller, it becomes a very key factor to various LEDs whether the epitaxial quality of various LEDs is even or not. For some manufacturing processes of display panels, micro LEDs are formed by the same epitaxial wafer in a chip manufacturing process and then transferred to a substrate having driving circuits therein by the mass transfer technology. In other words, there is no chance to additionally classify LEDs during the manufacturing process. Therefore, when these LEDs with different epitaxial qualities are disposed in the same display device, the image quality of the display device will be affected, and the yield rate of production will also decrease.